Taking a hydraulic power shovel type excavator as an example of hydraulic construction machine, it is largely constituted by a vehicular base carrier and an upper swing structure, along with a hydraulic motor for driving the vehicular base carrier and for putting the upper swing structure in swinging motions. Further, a working mechanism is provided on a hydraulic excavator of this sort. As a typical example, the working mechanism is put in operation for excavation of earth. The working mechanism is generally composed of a boom which is liftably supported on the upper swing structure, an arm which is pivotally connected to a fore distal end portion of the boom through a link mechanism, and a front attachment which is pivotally connected to a fore distal end portion of the arm through a link mechanism. These boom, arm and front attachment are respectively driven by a hydraulic cylinder.
As a hydraulic actuator, each one of the afore-mentioned hydraulic motor and hydraulic cylinders has one port connected to a hydraulic pump and the other port to an operating oil tank. Each hydraulic actuator is switchably connected either to the hydraulic pump or to the operating oil tank by way of a control valve which is operated by hydraulic pilot signals. In order to apply a hydraulic pilot signal to a hydraulic pilot portion of the control valve, a pilot valve is provided in association with the control valve. In this connection, it is the general practice to install a pilot valve on a top panel of a console box within a cab, on the right or left side of an operator's seat to be taken by an operator.
The pilot valve is largely composed of a pilot valve proper which is connected to hydraulic piping, and a manual operating means including an operating lever. Normally, the pilot valve proper is provided with an end plate which is fixed on one end of a valve casing. Erected on the end plate is a support shaft to which a manual operating lever is pivotally connected through a universal joint. An opening is formed in the top panel of the console box, to which the end plate is to be fixed. The pilot valve proper is located internally of the console box in such a way as to let the manual operating means protrude upward of the top panel of the console box. The operating lever is manually tilted in an arbitrary direction by an operator.
The casing of the pilot valve proper defines a valve chamber which accommodates at least a couple of spools for sliding movements in and along the valve chamber. A pair of pusher are connected to these spools and projected out of the end plate of the valve casing. The spools, which are connected with the respective pushers, are slidable within the valve chamber, in association with the paired pushers which are each abutted against a cam member which is attached on the operating lever. As the operating lever is manually tilted, one of the pushers and the spool which is connected with that pusher are caused to make a sliding displacement within the valve chamber, while the other pusher and spool are held standstill. Normally, the pilot valve proper is provided with a pair of pushers in combination with a pair of spools, and the operating lever is tiltable in a forward or rearward direction and in a rightward or leftward direction as well, putting one of the paired spools in action when the operating lever is tilted in a forward or rearward direction, and putting the other one of the paired spools in action when the operating lever is tilted in a rightward or leftward direction.
As a construction machine, a hydraulic power shovel type excavator is mainly resorted to for outdoor operations in a dusty environment where a large amount of dust flies in the air. Therefore, it is necessary to put on a dustproof member to prevent deposition of dust on engaging portions of the operating lever and spools and on the pilot valve proper. As a dustproofing member, a boot in the form of bellows of rubber or resilient material, as in Patent Literature 1, has thus far been in wide use. One end of the dustproofing boot is connected to an operating means, while the other end at the opposite end of an intermediate bellows section is connected to an end plate. The dustproofing boot which is made of a resilient material is provided as a replaceable member because it can be irrecoverably damaged. More specifically, one end of the boot is arranged to serve as a top end anchor portion which is detachably fixable to the side of a manual operating means, while the other end of the boot is arranged to serve as a root end anchor portion which is detachably fixable to the side of an end plate of a valve casing. Both of the top and root end anchor portions are formed in the shape of a thick annular lip.
In the pilot valve unit of Patent Literature 1, the opposite ends of a dustproofing boot are arranged as a top end anchor portion and a root end anchor portion to be fixed to an outer peripheral surface of a cam and an end plate, respectively. The top end anchor portion of the boot is fixedly fitted in annular stopper groove which is formed on an outer peripheral surface of the cam. Further, in order to form an annular stopper groove on a surface of the end plate, a mount plate is fixed on a surface of the end plate by welding in such a way as to form an annular stopper groove between the end plate and the stopper plate, receiving the root end anchor portion of the boot in this annular groove on the end plate.